WELDING PROCEDURES & QUALIFICATIONS Most of the people consider the welding qualifications as totally theoretical and hence it is not very uncommon to see people totally ignoring this aspect in a manufacturing set‐up. One would often meet several people in the related industries unaware of difference between a welding procedure qualification and a welder qualification. This paper is prepared with the intent of throwing light on aspects related to the welding qualifications. When an item is designed for a particular application, the material used for the construction of such an item is assumed to have certain properties. Mechanical strength and chemical composition are the two such properties that are considered very commonly in almost all the engineering designs. Naturally a weld joint which forms a part of the component also is assumed to have these properties. Due to the advancements in the Welding Technology and NDT methods it has been possible to obtain weld joints which are as strong as the parent material. Hence, these days, in most cases welds are considered to have the strength same as that of base material. To check that they have the desired properties, one can carry out any type of tests (either destructive or non‐destructive) for the parent metals, in most of the cases. But same is not the case with the weld metals. In most of the cases NDTs are the only methods available for testing the properties. But with NDTs one cannot determine the strength of the weld. Hence one would think of making a sample of the weld and test for the required properties. This would call for a testing, for every new job and every new joint. This is where the concept of welding procedures helps one to reduce the number of tests and hence the cost. WELDING PROCEDURE: A welder/ welding engineer must know several details before starting the welding, such as base material composition, thickness, process to be used, etc.. These details which a welder/ welding engineer must know before commencing welding are called Welding Variables. A document showing all the applicable welding variables is called WPS (Welding Procedure Specification). It is not enough if one has only the WPS. One must ensure that the weld made as per WPS meets all the requirements, which are nothing but the properties of the material of construction assumed by the designer while designing the item. Normally, the properties assumed are mechanical strength and chemical composition. Additionally it may also include notch toughness, hardness, corrosion resistance etc. How to ensure that the weld made have these properties? Weld a coupon as per WPS and test, if it meets the requirements one can assume that weld similarly made also will have similar properties. The document in which the actual values of the variables and the results of the test are recorded is called a PQR (Procedure Qualification Record). In other words, PQR is a record, which serves as a proof for the satisfactory performance of the weld made as per the specific WPS within the specific ranges permitted. The above process of testing to ensure the properties is called Procedure Qualification Test The WPS & PQR together constitute a Qualified Welding Procedure or in short a procedure. VI.Welding Procedures and qualifcations as Per ASME SEC IX Page 1 INTRODUCTION TO SEC IX OF ASME Throughout this paper a reference is made to ASME boiler and pressure vessel code for the sake of convenience. Accordingly the variables are classified under two groups. most of the codes call for a production weld coupons as an additional measure. in certain cases where lesser factor of safety is considered this may not be sufficient. The following points must clarify some of the doubts/ confusions commonly seen in the beginners. whose change results in the change in the properties are called as Essential Variables. But. What is required for a welder is skill to deposit sound weld metal by properly interpreting the welding procedure. It has been established that a change in the value of the variable need not necessarily change the properties. But the discussions are normally valid for any codes. whose change does not have any effect on the properties. one must view Welder Qualification more as a tool to get a repair free joint in the first instance. SEC IX of ASME covers various aspects relating to the welding qualifications. One must notice that welding procedure is only a mock up that can represent welding done in a shop under similar conditions. Variables. One must note that these production coupons themselves also act as qualification tests for the welding procedures. The process of testing the capability of the welder is known as "Welder Performance Qualification test". are called as Non‐Essential Variables. Just as a person capable of manipulating a steering wheel. These become essential variable when notch toughness is required for the weld as per applicable code. It is very much similar to a driving license issued to the drivers. can act as a driver. brakes. Whether it is required to carry out the testing for every new joint? No. a person capable of depositing sound weld metal can become a welder. VI. One must notice that most of the codes allow welder qualification on the job signifying the fact that what is important is the soundness of final weld. Variables are listed under one more head known as Supplementary Essential Variables. clutch etc. This authenticates a person to perform welding.Welding Procedures and qualifcations as Per ASME SEC IX Page 2 .. Hence. A document similar to driving license authorizing the driver to drive is the WPQ (Welder Performance Qualification record) for the welder. • • Variables. let us understand what is meant by the ‘qualification of the welding procedure'. Now that we know 'what a welding procedure is'. WELDER QUALIFICATION: Welder qualification is the second type of qualification required. Hence. Following Tips must help reader when reading the welding data: • • • Never read the welding data given in article IV unless called upon to do so by articles I. makes the reading easy VI. types and extent of discontinuities acceptable). Testing Procedures. 5 and 6 one must refer the Design code.Welding Procedures and qualifcations as Per ASME SEC IX Page 3 . welding and brazing. Specimen Details.1). Under ‘Welding’. 4. III Hence. Acceptance Criteria) etc.1. for example. Mainly covers • • Positions of welding Examinations (Various Types of Tests. 4. in addition to initial introduction. II or III Normally adding "a new qualification shall be done when …" before reading data against essential variable given in the tables of Article II and III(such as QW 253/6). This section does not specify Energy value for impact testing For points specified in 3. Format List of variables Qualified ranges Type and number of examinations required Article III ‐ Welding Performance Qualifications • • • • WPQ List of Variables Qualified ranges Type and number of examinations required Article IV ‐ Compiled welding data meant for using with articles I. Knowledge of how the contents (and their organization) of SEC IX should greatly help the readers to solve the commonly seen starting trouble. 2. 3. II. cross‐refers to this section This section does not guide in the selection of electrode This section does not guide in the design of joints This section does not specify the type and extent of radiography/ NDT to be used This section does not specify the acceptance criteria (i. makes the reading easy Normally adding "a new qualification is not required when …" before reading the data against non‐essential variable given in the tables of article II (such as QW 253/6). 5. one who wants to qualify a welder can directly refer article III. This section must be referred only when the design code (such as SEC VIII div. PQR Their contents. Article II ‐ Welding Procedure Qualifications • • • • • WPS. Article I: General. there are 4 chapters (Article I to IV). 6. This section has two parts.e. to reduce the number of qualification tests to be carried out. mfg. In the WPS it is enough if only P number and group number are specified. A simple example of usage of P number and group number is as follows A procedure qualified using a plates confirming to SA516 Gr.) are assigned a P number of 1. weldability mechanical properties etc.Thickness of the test coupon Thickness selection is the important and mostly confused parameter Welding procedure Following parameters shall be considered in the selection of thickness • • • Test coupon thickness Impact requirement Normalizing requirement ‐ governs the range ‐ governs the lower limit ‐ governs the upper limit Appendix‐I describes thickness selection in more detail. SA106. When they are not known. SA516 etc. if base material IS2062). Table QW422 lists the G numbers of various materials.. P stands for Parent metal. Welder’s Qualification One must preferably qualify a welder with a coupon of 20mm thickness or more which will qualify him to weld deposit of any thickness. material specification shall be written (ex. Grouping of materials Base materials and electrodes / filler materials are grouped variously due to their similarity of composition.60 can be used to weld a joint between the pipes confirming to SA106 Gr. QW422 and QW424 describe the rules for using the P numbers of qualifications. chemical composition shall be written. The latter options actually reduce the range qualified VI.Welding Procedures and qualifcations as Per ASME SEC IX Page 4 .. This will be an additional restriction on P number when impact testing is required for the base/ weld metal in the job specification. within a P number. G number This is a sub‐grouping of ferrous Base Materials having specified impact test requirements.B assuming that all other parameters remain unaffected. Below we will discuss few of them. Table QW422 lists the P numbers of various materials. With the help of P numbers the number of qualification tests required are greatly reduced. Base metals P number This is the grouping of Base Materials based on their chemical composition.. G stands for Group. For example all plain carbon steels (SA105. SA515. Practice etc. When specification also is not known. 'A' stands for weld metal Analysis. A change of filler metal (F number) needs a re‐qualification of welder VI.Welding Procedures and qualifcations as Per ASME SEC IX Page 5 . WPS/PQR • • • • • A procedure qualified using plates can be used for welding the pipes. GTAW. A procedure qualified using grove welds can be used for fillet welds of any size. in the procedure qualification test. These are described in QW430 A number This is the grouping of electrodes and filler materials based on the weld metal chemical composition. PQR. The format recommended by SEC IX. on normalizing can be used for welds made on equipment of SA516 Gr. Size of base metal. • • WPQ • • Normally a welder can be qualified using only a radiographic test. which has failed to meet the required tensile strength can be used for jobs with materials of lower strength. This can be used for the jobs having impact requirement or not Technically. A procedure qualified in any one position can be used to weld in any other position provided job specifications do not specify impact test. since. Weld metal becomes the Backing material. WPQ • • A double welded (welded from both the sides) joint is considered as a joint with backing. E7018 electrode. a procedure qualification test. F stands for F Filter metal. normally designated as T and size of weld deposit normally designated as t must be considered separately. commonly used for WPS/ PQR. These are described in QW440 Some facts relating to WPS. Hence. One must always carry out impact testing at the lowest possible temperature. SAW and GMAW. all other parameters remain same A test coupon of thickness 40mm used for procedure qualification test covers largest range from 5 mm to 200mm (without heat treatment or impact requirements).70.60. some of the points are not applicable for some processes. For example. provided the P number ‐ G number criteria is met. provided. if the tensile test results showed a value of 65 ksi when tested with a coupon material of SA516 Gr. one must be careful when using them. is common for processes SMAW. Filler materials F number This is the grouping of electrodes and filler materials based on their usability characteristics mainly governed by flux or shielding medium used (which also govern their electrical characteristics). • • Presence or absence of impact test or normalizing does not affect the welder's skill and hence the qualification.Welding Procedures and qualifcations as Per ASME SEC IX Page 6 . VI. Hence. a welder qualified on lower diameters can always weld higher diameters (plate is a pipe with infinite diameter). A small diameter pipe requires more skill for welding. Welding Procedures and qualifcations as Per ASME SEC IX Page 7 Reference 16 SS CS 32 Process (assumption) ‐ 2 layers (root and hot pass) of GTAW and rest by SMAW (fill‐up and final). limited within the range of qw‐451 *********** VI. proceed to welding data such as QW‐403.8 8.8 (as specified in the tables) and then proceed to QW‐451(as specified in the data) and select the thickness in such a way as to cover the largest range. code does not permit dissimilar thickness for the test coupon Step 2: Choose 16mm (arbitrary). however. Thickness of the thinner member shall be as permitted by QW‐451 2. various steps to be followed to arrive at the optimum thickness are as follows. One may.4 (due to normalizing) ‐ 18 8. Let us take an example to illustrate the above point.2 indirectly restrains us from choosing a thickness varying too much from that of job. max From To GTAW SMAW As per QW‐450 (Based on Thickness of the coupon) 5 64 64 64 As per QW‐407. Unlimited for specified material provided a) Materials are of same P number.4 (due to normalizing) ‐ 35 35 35 As per QW‐403. max From To GTAW SMAW As per QW‐450 (Based on Thickness of the coupon) 5 32 16 16 As per QW‐407.Appendix I Determination of test coupon thickness for welding procedure qualification Ideally one must start with tables such as QW‐253/256.8 8. Step 1: Start with thickness same as the job. For the joint configuration shown on the right. b) qualification is made on >¼” ii.6 (due to impact test requirement) 16 ‐ ‐ ‐ Result 16 18 8. choose any thickness higher than 32 mm.8 Step 3: Choose 32 mm (arbitrary).8 As per QW‐403. Heat treatment ‐ Normalizing Min. Additionally QW407. This will qualify us for Thickness T of base metal t of weld metal. but this would not yield any additional benefit due to the presence of normalizing in the job requirement in this example. But. ‐ 48ºC . What happens when a production weld has two dissimilar metal thicknesses? This shall be arrived at in two steps 1.6 (due to impact test requirement) 16 ‐ ‐ ‐ Result 16 35 35 35 One must note that the step 3 gives us the largest range. Reference Thickness T of base metal t of weld metal. Thickness of the thicker member shall be i. This will qualify us for. design temperature.
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